This invention relates to an improved vehicle crash cushion for decelerating and redirecting a vehicle, for example a vehicle that has left a roadway.
Crash cushions are commonly employed alongside roadways to stop a vehicle, which has left the roadway, in a controlled manner while limiting the maximum deceleration to which the occupants of the vehicle are subjected. Non-gating or redirective crash cushions have sufficient strength to redirect a laterally impacting vehicle when struck from the side in a lateral impact. One criteria for measuring the capabilities of a crash cushion is the crash test specification-n NCHRP 350. Under the tests in this specification, an occupant of both light and heavy vehicles must experience less than a 12 m/s change in velocity (delta (Δ) V) upon contacting the vehicle interior and less than a 20 g deceleration after contact.
Often, in non-gating/redirecting types of crash cushions, the structure that absorbs energy in an axial impact does not also function to redirect a vehicle impacting the side of the system. Accordingly, additional structures must be provided to resist the lateral impact, for example fender panels, as well as to anchor or resist lateral movement, for example cables or tracks. Such multiple assembly structures can be expensive to make and time consuming to install.
In addition, many of these systems are not bi-directional, meaning they do not adequately redirect vehicles striking the crash cushion on opposite sides when traveling in opposite directions.
One crash cushion shown in U.S. Pat. No. 3,674,115 to Young, assigned to Energy Absorption Systems, Inc., the assignee of the present invention, includes a frame made up of an axially oriented array of segments, each having a diaphragm extending transverse to the axial direction and a pair of side panels positioned to extend rearwardly from the diaphragm. Energy absorbing elements (in this example water filled flexible cylindrical elements) are mounted between the diaphragms. During an axial impact the diaphragms deform the energy absorbing elements, thereby causing water to be accelerated to absorb the kinetic energy of the impacting vehicle. Axially oriented cables are positioned on each side of the diaphragms to maintain the diaphragms in axial alignment during an impact.
U.S. Pat. No. 3,944,187 and U.S. Pat. No. 3,982,734 to Walker, both assigned to Energy Absorption Systems, Inc., the assignee of this invention, also include a collapsible frame made up of an axially oriented array of diaphragms with side panels mounted to the diaphragms that slide over one another during an axial collapse. Energy absorbing cartridges perform the energy absorption function, while obliquely oriented cables are provided between the diaphragms and ground anchors to maintain the diaphragms in axial alignment during a lateral impact.
U.S. Pat. No. 4,452,431 to Stephens, also assigned to Energy Absorption Systems, Inc., the assignee of the present invention, shows yet another collapsible crash barrier employing diaphragms and side panels generally similar to those described above. This system also uses axially oriented cables to maintain the diaphragms in axial alignment, as well as breakaway cables secured between the front diaphragm and the ground anchor. These breakaway cables are provided with shear pins designed to fail during an axial impact to allow the frame to collapse.
U.S. Pat. No. 4,399,980 to VanSchie discloses another crash barrier which employs cylindrical tubes oriented axially between adjacent diaphragms. The energy required to deform these tubes during an axial collapse provides a force tending to decelerate the impacting vehicle. Cross-braces are used to stiffen the frame against lateral impacts, and a guide is provided for the front of the frame to prevent the front of the frame from moving laterally when the frame is struck in a glancing impact by an impacting vehicle.
In yet another system, shown in U.S. Pat. No. 6,293,727, the crash cushion includes frames connected with side panels, and an energy absorbing device that includes a cutter that cuts through a metal plate. A sled is supported by guide rails, which resist lateral impacts.
All of these prior art systems are designed to absorb the kinetic energy of the impacting vehicle by deforming an energy absorbing structure. These systems use additional structural members that resist side forces.
U.S. Pat. No. 5,022,782 to Gertz et al., also assigned to Energy Absorption Systems, Inc., the assignee of the present application, shows another crash barrier using a friction brake to dissipate energy. The system also includes peel straps connecting fender panels, with the peel straps absorbing energy during a collision.
Another system is shown in PCT Application WO 03/102402A2, which discloses a crash cushion using an adjustable array of pins to deform strips or tubes to dissipate energy. The energy required to deform the strips or tubes results in a kinetic energy dissipating force which decelerates the impacting vehicle. The system pushes the array of pins along the strips or tubes, and the strips and/or tubes do not provide redirective capabilities. Other systems showing the principle of deforming metal to absorb energy are shown for example in U.S. Pat. No. 4,223,763, to Duclos et al. and U.S. Pat. No. 3,087,584 to Jackson.
Another system is shown in U.S. Pat. No. 6,719,483 to Welandson, which discloses a forming device that deforms a crash barrier girder. The girder is secured to post members that are not moveable, but rather are anchored in the ground.
Thus, a need presently exists for an improved highway crash barrier that provides predictable decelerating forces to an axially impacting vehicle, that is low in cost, that is simple to install, that minimizes the structure required to resist lateral impacts, that is bi-directional and that efficiently redirects laterally impacting vehicles.